Blender Grease Pencil

---
name: blender-grease-pencil
description: >-
  Create 2D art and animation in Blender using Grease Pencil and Python. Use
  when the user wants to draw strokes programmatically, create 2D animations,
  build Grease Pencil objects from code, manage GP layers and frames, apply GP
  modifiers, set up drawing guides, or script any Grease Pencil workflow in
  Blender.
license: Apache-2.0
compatibility: >-
  Requires Blender 3.0+. Grease Pencil v3 API available in Blender 4.0+.
  Run: blender --background --python script.py
metadata:
  author: terminal-skills
  version: "1.0.0"
  category: design
  tags: ["blender", "grease-pencil", "2d-animation", "drawing", "strokes"]
---

# Blender Grease Pencil

## Overview

Create 2D drawings and animations in Blender's 3D space using the Grease Pencil system and Python. Build strokes from point data, manage layers and frames, apply GP-specific modifiers, and animate 2D content — all scriptable from the terminal.

## Instructions

### 1. Create a Grease Pencil object

```python
import bpy

# Create a new Grease Pencil data block and object
gp_data = bpy.data.grease_pencils.new("MyDrawing")
gp_obj = bpy.data.objects.new("MyDrawing", gp_data)
bpy.context.collection.objects.link(gp_obj)

# Or use the operator
bpy.ops.object.gpencil_add(type='EMPTY')  # EMPTY, STROKE, MONKEY, SCENE, COLLECTION
gp_obj = bpy.context.active_object
```

Types for `gpencil_add`: `EMPTY` (blank), `STROKE` (single stroke), `MONKEY` (Suzanne in 2D), `SCENE` (draw over scene), `COLLECTION` (from collection).

### 2. Add layers and frames

```python
import bpy

gp_data = bpy.context.active_object.data

# Create a layer
layer = gp_data.layers.new("Outlines", set_active=True)
layer.info = "Outlines"
layer.blend_mode = 'REGULAR'  # REGULAR, OVERLAY, ADD, SUBTRACT, MULTIPLY
layer.opacity = 1.0
layer.use_lights = False

# Create a keyframe on the layer at a specific frame
frame = layer.frames.new(frame_number=1)

# Additional layers for organization
color_layer = gp_data.layers.new("Colors", set_active=False)
color_frame = color_layer.frames.new(frame_number=1)
```

### 3. Draw strokes programmatically

```python
import bpy

gp_obj = bpy.context.active_object
gp_data = gp_obj.data
layer = gp_data.layers.active
frame = layer.frames[0]  # or layer.active_frame

# Create a stroke
stroke = frame.strokes.new()
stroke.display_mode = '3DSPACE'  # 3DSPACE, 2DSPACE, 2DIMAGE, SCREEN
stroke.line_width = 10

# Add points to the stroke
num_points = 5
stroke.points.add(num_points)

coords = [(0, 0, 0), (1, 0.5, 0), (2, 1, 0), (3, 0.5, 0), (4, 0, 0)]
for i, (x, y, z) in enumerate(coords):
    stroke.points[i].co = (x, y, z)
    stroke.points[i].pressure = 1.0      # pen pressure (0.0 - 1.0)
    stroke.points[i].strength = 1.0      # color strength (0.0 - 1.0)

# Assign material index to stroke
stroke.material_index = 0
```

### 4. Create GP materials

```python
import bpy

gp_obj = bpy.context.active_object

# Solid fill material
mat_solid = bpy.data.materials.new("GP_Solid")
bpy.data.materials.create_gpencil_data(mat_solid)
mat_solid.grease_pencil.color = (0.1, 0.1, 0.1, 1.0)       # stroke color
mat_solid.grease_pencil.fill_color = (0.8, 0.2, 0.2, 1.0)  # fill color
mat_solid.grease_pencil.show_fill = True
mat_solid.grease_pencil.show_stroke = True
gp_obj.data.materials.append(mat_solid)

# Line-only material
mat_line = bpy.data.materials.new("GP_Line")
bpy.data.materials.create_gpencil_data(mat_line)
mat_line.grease_pencil.color = (0.0, 0.0, 0.0, 1.0)
mat_line.grease_pencil.show_fill = False
mat_line.grease_pencil.show_stroke = True
gp_obj.data.materials.append(mat_line)
```

### 5. Apply Grease Pencil modifiers

```python
import bpy

gp_obj = bpy.context.active_object

# Thickness modifier
thick = gp_obj.grease_pencil_modifiers.new("Thickness", 'GP_THICK')
thick.thickness_factor = 1.5

# Smooth modifier
smooth = gp_obj.grease_pencil_modifiers.new("Smooth", 'GP_SMOOTH')
smooth.factor = 0.5
smooth.step = 3

# Tint modifier (color shift)
tint = gp_obj.grease_pencil_modifiers.new("Tint", 'GP_TINT')
tint.color = (0.2, 0.5, 1.0)
tint.factor = 0.3

# Noise modifier (hand-drawn look)
noise = gp_obj.grease_pencil_modifiers.new("Noise", 'GP_NOISE')
noise.factor = 0.5

# Subdivide modifier (smoother curves)
subdiv = gp_obj.grease_pencil_modifiers.new("Subdivide", 'GP_SUBDIV')
subdiv.level = 2

# Build modifier (animated reveal)
build = gp_obj.grease_pencil_modifiers.new("Build", 'GP_BUILD')
build.mode = 'SEQUENTIAL'  # SEQUENTIAL, CONCURRENT, ADDITIVE
build.start_frame = 1
build.length = 50

# Array modifier (repeat strokes)
array = gp_obj.grease_pencil_modifiers.new("Array", 'GP_ARRAY')
array.count = 5
array.offset = (1.0, 0.0, 0.0)
```

### 6. Animate Grease Pencil frame by frame

```python
import bpy
import math

gp_obj = bpy.context.active_object
gp_data = gp_obj.data
layer = gp_data.layers.active

total_frames = 24

for f in range(total_frames):
    frame = layer.frames.new(frame_number=f + 1)

    stroke = frame.strokes.new()
    stroke.display_mode = '3DSPACE'
    stroke.line_width = 8

    # Animate a circle that grows
    num_points = 32
    stroke.points.add(num_points)
    radius = 0.5 + (f / total_frames) * 2.0

    for i in range(num_points):
        angle = (2 * math.pi * i) / num_points
        x = radius * math.cos(angle)
        y = radius * math.sin(angle)
        stroke.points[i].co = (x, y, 0)
        stroke.points[i].pressure = 1.0
        stroke.points[i].strength = 1.0

# Set playback range
bpy.context.scene.frame_start = 1
bpy.context.scene.frame_end = total_frames
```

### 7. Configure drawing guides

```python
import bpy

# Guides are properties on the scene's tool settings
ts = bpy.context.scene.tool_settings
gp_settings = ts.gpencil_sculpt

# Access guide settings (when in Draw mode)
guide = ts.gpencil_stroke_placement_view3d

# Guide types are set via the tool settings
# Circular — concentric rings from reference point
# Radial — rays extending from reference point
# Parallel — constrained parallel lines
# Grid — horizontal/vertical grid lines
# Isometric — isometric angle constraints

# Note: Guides are interactive Draw mode features.
# For programmatic geometry, compute constrained points directly:
import math

def snap_to_grid(point, spacing=1.0):
    return tuple(round(c / spacing) * spacing for c in point)

def snap_to_radial(point, center=(0, 0, 0), num_rays=8):
    dx, dy = point[0] - center[0], point[1] - center[1]
    angle = math.atan2(dy, dx)
    snap_angle = round(angle / (2 * math.pi / num_rays)) * (2 * math.pi / num_rays)
    dist = math.sqrt(dx**2 + dy**2)
    return (center[0] + dist * math.cos(snap_angle),
            center[1] + dist * math.sin(snap_angle),
            point[2])
```

## Examples

### Example 1: Procedural comic panel with text

**User request:** "Create a simple comic panel layout with borders and speech bubble"

```python
import bpy
import math

def clear_scene():
    bpy.ops.object.select_all(action='SELECT')
    bpy.ops.object.delete()

clear_scene()

# Create GP object
gp_data = bpy.data.grease_pencils.new("ComicPanel")
gp_obj = bpy.data.objects.new("ComicPanel", gp_data)
bpy.context.collection.objects.link(gp_obj)

# Materials
mat_black = bpy.data.materials.new("GP_Black")
bpy.data.materials.create_gpencil_data(mat_black)
mat_black.grease_pencil.color = (0, 0, 0, 1)
mat_black.grease_pencil.show_fill = False
gp_obj.data.materials.append(mat_black)

mat_bubble = bpy.data.materials.new("GP_Bubble")
bpy.data.materials.create_gpencil_data(mat_bubble)
mat_bubble.grease_pencil.color = (0, 0, 0, 1)
mat_bubble.grease_pencil.fill_color = (1, 1, 1, 1)
mat_bubble.grease_pencil.show_fill = True
gp_obj.data.materials.append(mat_bubble)

# Panel border layer
border_layer = gp_data.layers.new("Borders")
border_frame = border_layer.frames.new(frame_number=1)

def draw_rect(frame, x, y, w, h, mat_idx=0, width=12):
    stroke = frame.strokes.new()
    stroke.display_mode = '3DSPACE'
    stroke.line_width = width
    stroke.material_index = mat_idx
    stroke.points.add(5)
    corners = [(x, y, 0), (x+w, y, 0), (x+w, y+h, 0), (x, y+h, 0), (x, y, 0)]
    for i, co in enumerate(corners):
        stroke.points[i].co = co
        stroke.points[i].pressure = 1.0
        stroke.points[i].strength = 1.0

# Outer border
draw_rect(border_frame, 0, 0, 6, 4)
# Inner panels (2 panels side by side)
draw_rect(border_frame, 0.2, 0.2, 2.7, 3.6)
draw_rect(border_frame, 3.1, 0.2, 2.7, 3.6)

# Speech bubble layer
bubble_layer = gp_data.layers.new("Bubbles")
bubble_frame = bubble_layer.frames.new(frame_number=1)

stroke = bubble_frame.strokes.new()
stroke.display_mode = '3DSPACE'
stroke.line_width = 6
stroke.material_index = 1
num_pts = 24
stroke.points.add(num_pts)
cx, cy, rx, ry = 4.5, 3.0, 0.8, 0.4
for i in range(num_pts):
    angle = (2 * math.pi * i) / num_pts
    stroke.points[i].co = (cx + rx * math.cos(angle), cy + ry * math.sin(angle), 0)
    stroke.points[i].pressure = 1.0
    stroke.points[i].strength = 1.0

bpy.ops.wm.save_as_mainfile(filepath="/tmp/comic_panel.blend")
```

### Example 2: Animated handwriting effect

**User request:** "Create an animation that draws text stroke by stroke like handwriting"

```python
import bpy

def clear_scene():
    bpy.ops.object.select_all(action='SELECT')
    bpy.ops.object.delete()

clear_scene()

bpy.ops.object.gpencil_add(type='EMPTY')
gp_obj = bpy.context.active_object
gp_data = gp_obj.data

# Material
mat = bpy.data.materials.new("GP_Ink")
bpy.data.materials.create_gpencil_data(mat)
mat.grease_pencil.color = (0.05, 0.05, 0.15, 1)
gp_data.materials.append(mat)

layer = gp_data.layers.active
frame = layer.frames.new(frame_number=1) if not layer.frames else layer.frames[0]

# Define letter paths as point sequences (simplified "HI")
letters = {
    'H': [(0,0,0),(0,2,0),(0,1,0),(1,1,0),(1,2,0),(1,0,0)],
    'I': [(2.5,2,0),(2.5,0,0)],
}

for letter, points in letters.items():
    stroke = frame.strokes.new()
    stroke.display_mode = '3DSPACE'
    stroke.line_width = 10
    stroke.material_index = 0
    stroke.points.add(len(points))
    for i, co in enumerate(points):
        stroke.points[i].co = co
        stroke.points[i].pressure = 1.0
        stroke.points[i].strength = 1.0

# Add Build modifier for animated reveal
build = gp_obj.grease_pencil_modifiers.new("Build", 'GP_BUILD')
build.mode = 'SEQUENTIAL'
build.start_frame = 1
build.length = 60

bpy.context.scene.frame_start = 1
bpy.context.scene.frame_end = 60

bpy.ops.wm.save_as_mainfile(filepath="/tmp/handwriting.blend")
```

## Guidelines

- Use `bpy.data.grease_pencils.new()` for data-level creation. Use `bpy.ops.object.gpencil_add()` for quick object creation with defaults.
- Always create at least one material and assign it before rendering — GP objects without materials render invisible.
- Stroke `display_mode` controls coordinate space: `3DSPACE` for world-space strokes, `2DSPACE` for screen-relative. Use `3DSPACE` for most scripted workflows.
- The `pressure` property on points controls line thickness variation. Set to 1.0 for uniform width, vary between 0.0-1.0 for pen-like tapering.
- GP modifiers use `grease_pencil_modifiers` (not `modifiers`). Type constants are prefixed with `GP_` (e.g., `GP_THICK`, `GP_SMOOTH`).
- For frame-by-frame animation, create separate `layer.frames.new(frame_number=N)` entries. Each frame holds independent strokes.
- The Build modifier is the easiest way to animate stroke reveal without per-frame scripting.
- Grease Pencil objects support the same transform operations as mesh objects (location, rotation, scale, parenting, constraints).
- For complex 2D art, organize content across multiple layers (outlines, fills, colors, effects) just like in traditional digital art software.